VARIANT Structure

05/31/2018

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Most of the Microsoft Active Accessibility functions and the IAccessible properties and methods take a VARIANT structure as a parameter. Essentially, the VARIANT structure is a container for a large union that carries many types of data.

The value in the first member of the structure, vt, describes which of the union members is valid. Although the VARIANT structure supports many different data types, Microsoft Active Accessibility uses only the following types.

vt Value

Corresponding value member name

VT_I4

lVal

VT_DISPATCH

pdispVal

VT_BSTR

bstrVal

VT_EMPTY

none

When you receive information in a VARIANT structure, check the vt member to find out which member contains valid data. Similarly, when you send information using a VARIANT structure, always set vt to reflect the union member that contains the information.

Before using the structure, initialize it by calling the VariantInit Component Object Model (COM) function. When finished with the structure, clear it before the memory that contains the VARIANT is freed by calling VariantClear.